Chapter Images shutterstock.com 7 Water: The Universal Solvent

Chapter

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7Water:

The Universal Solvent

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

Objectives

• Describe how the structure of a water molecule affects water’s physical characteristics.

• Demonstrate a function of water in food preparation.

• Explain how the water content of food affects how the food will react during preparation and storage processes.

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Objectives

• Identify four functions of water in the body.

• List common contaminants in water.


Water

• Water is– the only substance found in abundance

in the solid, liquid, and gaseous state– the main component of many foods– a nutrient necessary to sustain life

• Nutritionally, water– helps control body temperature– transports nutrients and waste products– provides the solution for metabolic

reactions continued


Water

• Water also– influences the texture, appearance, and

taste of food– is an important heat medium in cooking– is an important solvent for cleaning and

sanitation– is critical in food preservation– determines the likelihood of food

spoilage by its presence or absence


Types of Covalent Bonds

• Water (H2O) has 2 hydrogen atoms and one oxygen atom – held together by covalent bonds

• A nonpolar covalent bond is electrically neutral since electrons are shared equally by the atoms in the molecule

• Water has a polar covalent bond, or an unequal sharing of electrons


Hydrogen Bonds

• The positive hydrogen end of one water molecule is drawn to the negative oxygen ends of other water molecules– This forms a hydrogen bond that is

intermolecular, or between molecules

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Surface Tension

• Hydrogen bonds in water create a greater surface tension than most compounds, allowing water to – cling to something else as well as itself– have a higher melting and boiling point

than other compounds– freeze faster than it thaws– form a crystalline structure in the solid

state

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Surface Tension

• Hydrogen bonding helps to dissolve polar substances, making water a great solvent– Sugars, starches,

and proteins form hydrogen bonds with water

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Pressure, Temperature, and Phase Changes• Atmospheric pressure impacts the

boiling and freezing points– Water boils at lower temperatures at high

altitudes and at higher temperatures at low altitudes

– High altitude baking considerations such as increasing the amount of flour, water content, and oven temperature need to be considered


Impact of Impurities in Water• Water is not usually found in pure

form because it is such a great solvent

• An impurity in water may change its– physical and chemical characteristics– flavor and color– boiling and freezing points– hydrogen bonding


Functions of Water in Food Preparation• Water transfers heat energy into food

– Water boils at a constant temperature– Steam is as hot as boiling water when

not under pressure, but is hotter under pressure

• Steam– leaves food more flavorful and nutritious

than boiling– leavens baked goods

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Functions of Water in Food Preparation• Gas-in-water solutions

– Carbon dioxide is the gas solute dissolved in water when making carbonated beverages

– Oxygen also dissolves in water and is partially responsible for the taste of water

• Liquid-in-water solutions– Alcoholic beverages, vinegars and fruit

juice concentrates are examplescontinued


Functions of Water in Food Preparation• Solid-in-water solutions

– If a solid is dissolved in water, the chemical properties will be different than pure water

– Salt and sugar lower the freezing point and increase the boiling point of water

– Tea and coffee are flavor compounds dissolved in water


Water Content in Foods

• Water is a major part of most foods– Fruits and vegetables are over 70% water

– Bread is 36% water

– Popcorn is 4% water

continued©Aprilphoto/Shutterstock.com



• Water becomes part of the structure of food in 3 ways

1. Free water – is easily separated from food tissue– often contains dissolved compounds– boils and freezes easily– readily evaporates when foods are dried

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2. Bound water – is tied to the structure of larger

molecules– does not easily freeze or boil– chemically reacts as part of the larger

molecule

3. A hydrate– is any compound loosely bound with

water– must be boiled to be free of water,

known as anhydrouscontinued



• The water type impacts perishability– Water bound to other compounds is not

available to support food spoilage– Water in carrots is mostly bound to starch

molecules, while in milk, it’s mostly free– Both are 88% water, but carrots are

much less perishable

continued©Dionisvera/Shutterstock.com ©Jozsef

Szasz-Fabian/Shutterstock.com



• Water activity (Aw) takes into account the water available to support enzyme activity and microorganism growth– It is measured in values from 0 to 1– The higher the number is, the more

perishable the food will be– Canned foods are much more perishable

than dried


Functions of Water in the Body• The 4 main functions of water in the

body are to– maintain body temperature– transport nutrients and waste products– serve as a reactant in metabolism– become part of body tissue

• The water you drink and the water found in foods you eat help you stay hydrated


A Safe Water Supply

• Rainwater that enters lakes and rivers may be filtered to become drinking water

• A contaminant or pollutant is anything that makes a substance like water impure or unsafe, such as– human and animal wastes– chemicals and factory waste– garbage


Common Pollutants

• Biological contaminants– Large numbers of bacteria, protozoa,

viruses, and organic waste deplete oxygen from rivers, lakes, and water supplies

• Chemical contaminants– Metal ions such as calcium or magnesium

cause hard water– Acid rain changes the pH of water

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Common Pollutants

• Physical contaminants– Garbage and litter such as cans, bottles,

and plastics harbor bacteria, cause physical harm, and break down into toxins that enter the water supply

©Ariene Studio/Shutterstock.com


• The structure of water gives it many unique characteristics and functions in the human body and in food production

• In food preparation, water acts as a – heat medium– leavening agent in baked goods when

in the gaseous phase– solvent of gases, liquids, and solids

Recap

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• Water becomes part of the structure of food in the form of– free water– bound water– a hydrate

• Foods with higher water activity (AW) better support enzyme activity and microorganism growth

Recap

continued


• Water is necessary in the body to– maintain body temperature– transport nutrients– serve as a reactant in metabolism– become part of body tissues

• Common contaminants in water are– biological pollutants such as bacteria– chemical contaminants such as metal

ions– physical contaminants such as litter

Recap

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Chapter Images shutterstock.com 7 Water: The Universal Solvent